Envy isn't limited only to humans

A study conducted by the University of Vienna in Austria has found that dogs experience an emotion similar to envy when other dogs get a better reward, according to an article in the Washington Post.

The study investigated the reactions of dogs when they, and dogs around them, were given a reward of either bread or meat for performing a simple trick, like offering a paw. The researchers found that the deprived dogs, who received bread as a treat, would start to act frustrated; they were slower to respond to commands, scratch themselves, lick their mouths, and yawn.

So far, the only animals who are known to exhibit an envy-like behavior besides humans were monkeys and chimpanzees.